I really thought I was going to miss mac's Quick Look.
In my preliminary research, it seemed to be clear that there was no real replacement for it, currently, in the Linux world. There were, as the op found, a couple of "hit the space bar and get a preview" options in various file managers - but none that let you move through a directory the way mac can.
I can't speak for the other desktops but with KDE Plasma (I imagine that many of the others have something comparable) There is Gwenview which is almost as seamless. Once you double click on a single picture, the image opens in a browsing window and you can now easily browse, with your arrow keys, any of the other images in that directory, the way Quick Looks does. The difference is you now have a stand alone app open (although its a very lightweight, fast to open and close application). If you want to browse another folder, you can pretty fluidly navigate to it within Gwenview. You, also, can have multiple instances of it open and browse through several directories at once.
While it's not quite the same methodology as Quick Look, I'm finding it fills the function just as nicely - at least for my needs (and in some ways it's less annoying because, on a mac, as I am previewing an image, I frequently find myself unconsciously reaching to open something else and, ooops, Quick Look has followed me and I'm no longer looking at my photo - my own form of helplessness to be sure, but I do it all the time).
The other piece that KDE does to help fill the void is the fact that, with its default Dolphin File Manager, you can get a large preview (and a wealth of other info if you choose) of your file in any view mode, even list view (which OS Finder does not give you - you have to be in the often hated Column view to get this). This preview changes as you browse. It works with video as well. A keyboard shortcut can toggle this big preview panel on and off.
Out of the box, it doesn't look into documents the way Quick Look does but there are plugins for that. I just haven't gotten to them yet.
As for general file browsing and multitasking, I'm also finding KDE plasma to be an easier, less cumbersome experience then OSX. Once I learned the key shortcuts, the whole process of juggling windows has been, actually, more pleasant than on a Mac. (That said, I've recently discovered the Moom app for Mac, which helps a lot with window management, but I still am prefering Dolphin on Linux).
- One of my favorite things, so simple really, I don't have to have the mouse cursor on a corner of a window to scale, or on the title bar to move it. My cursor can be anywhere on the window, I just have to hold down ALT (ALT + RT MOUSE BUTTON to scale, ALT + LT MOUSE to move). I can't express in words how handy this tiny feature is for a window multitasker like myself. There is, of course, also, the expose-like present all windows, and toggle between all open tasks, keyboard shortcuts as well.
Anyway, while I guess I'm turning into a KDE fan-boy, I'll say this about my experience with Linux as a whole: Compared to Mac, there are a larger percentage of things that are not up and running out of the box (having everything just work is, of course, one of Mac's most defining, most ingenious qualities). However, with some additional tinkering, the functionality (and good looks) is there...and then some. What I appreciate (and this is why I think I was destined to be a Linux nerd) is the ability to make it my own.
